Method for lubricating compressed air tools and a lubricating oil for carrying out the method



United States Patent 3,277,005 METHOD FOR LUBRICATING COMPRESSED AIR TOOLS AND A LUBRICATING OIL FOR CARRY- ING OUT THE METHOD Dan Allan Petrini, Hammarbacken 13, Danderyd, Sweden No Drawing. Filed June 4, 1963, Ser. No. 285,233 Claims priority, application Sweden, June 6, 1962, 6,363/62 7 Claims. (Cl. 252-56) The present invention is concerned with a method for lubricating compressed air tools and a lubricating oil for carrying out the method.

The lubrication of compressed air tools, which term is here primarily intended for drills or similar tools for rock drilling, is effected in such a manner that the compressed air supplied to the tool is contacted with a lubricating oil under such conditions as to suspend a quantity of the lubricating oil sufficient for the lubricating process in the form of fine drops in the air stream, whereupon the oil is carried with this stream to the movable parts of the compressed air tool which are to be lubricated, where also the expansion of the compressed air while carrying out a work takes place. In connection with the expansion, the temperature of the air will be strongly lowered which results in the temperature of the oil being also lowered. An important requirement which has to be put on a lubricating oil for a compressed air tool is, therefore, that it should have low cloud and pour points and, in addition thereto, also a high viscosity index. As a matter of fact, these requirements have to be increased if the compressed air tool is to be used at low outdoor temperatures. Because mineral oils are a mixture of hydrocarbons, it will be difficult to combine these properties with each other in one oil. This is ascribed to the fact that hydrocarbon compositions giving a high index of viscosity also give high cloud and pour points. Tests carried out with lubricating oils on pure mineral oil basis have, however, proved that the ideal field of viscosity of a compressed air tool is considerably narrower than that within which the oil viscosity will move, due to variations of the temperature of atmosphere. Such oils have also proved to possess certain properties negative from lubrication viewpoint that can be related to the fact that the mineral oil lacks stabile flowing properties within the range of temperature which comes in question for the compressed air tools. This may result in an undercooling of the oil and to jumping increases of viscosity of the latter due to the precipitation of certain hydrocarbons occurring in mineral oils, for example, paraflins. It is apparently the precipitated hydrocarbons that are responsible for the impaired lubrication and other disturbances occurring.

According to the present invention, it has been found that diesters of dibasic aliphatic and, but to a somewhat less degree, also cycloaliphatic carboxylic acids, containing from 6 to 10 inclusive carbon atoms, as substances more unitary from chemical viewpoint, the cloud and pour points of which are nearer to each other or, in the limiting case, agree with each other, when used in compressed air tools, effect a lubrication of the movable parts of the compressed air tools superior to what is attained with mineral oils, at the low temperatures which come in question. This is ascribed, among other things, to the diesters, as being substances more unitary from chemical viewpoint, possessing stabile flowing properties right down to the pour point, whereby underfreezings and increases of viscosity are avoided. By using the preferable dependence of the viscosity of the diesters upon the temperature, it will be possible to narrow the field of viscosity, within which, due to variations of the "Ice outdoor temperature, the oil moves, so that this field coincides with the field of viscosity ideal for the appropriate tool. According to the invention, there is thus used for the lubrication a lubricating medium or oil comprising one or more such esters. In this connection, it has proved that the content of the esters of the lubricating oil should usually amount to at least 25 percent, preferably at least 35 percent.

On the other hand, it has proved that the content of the esters should not be too high a one which is ascribed to a dillerent circumstance. In dispersing pure esters or lubricating mediumshaving a relatively high content of the esters with air, there will readily be formed drops, the sizes of which are too uniform to deposit satisfactorily on the surfaces to be lubricated. If the esters are, however, diluted with a mineral oil having suitable properties, there will be formed after the dispersion of the mixture with air a suspension of drops, the sizes of which are more diifering, so that they deposit more readily on the surfaces to be lubricated. According to the invention, a lubricating oil is, therefore, used, the content of the esters set forth of which is preferably not over ca percent, more preferably not over about 70 percent.

As diesters of dibasic acids, containing from 6 to 10 inclusive carbon atoms, may primarily be mentioned diesters of adipic acid, pimelic acid, azelaic acid, sebacic acid and pinic acid (3-carboxy-2,2-dimethyl cyclobutane acetic acid). Except the pinic acid, which is a dibasic cycloaliphatic acid, it is thus the question of dibasic aliphatic acids having each a straight, saturated carbon chain. The esters of these acids that have proved most suitable are the alkyl esters, that is, esters formed from alkanols. According to the invention, these alkanols may either be straight-chained or have a branched chain, and the number of carbon atoms should exceed the value 5. Esters which have proved suitable are, for example, those of the acids set forth with the different hexanols, such as n-hexanol and 2-propylpropanol-(1), the different heptanols, such as n-heptanol, heptanol-(3) and 5-methyl-hexanol-(3), the different octanols, such as 2-ethylhexanol-(1) and iso-octanol, the nonylalcohols, such as n-nonanol, the decylalcohols, such as n-decanol, the undecanols, such as n-undecanol, and also higher alcohols.

In the lubricating oil according to the invention may also be incorporated one or more hydrophobing agents. Examples of these agents are lecithin and Lubrisol 541. The object of this addition, which may amount to about 1 percent, but which does not usually exceed 0.5 percent, is to provide hydrophobic coatings on the metal surfaces of the compressed air tools. Ice crystals formed in the expansion of the pressure air are hereby prevented from depositing on the surfaces with accompanying less risks that the compressed air tool will clog.

The mineral oil which is mixed with the diesters of dibasic acids to provide the lubricating medium of the invention, should be a high antifreezing quality spindle oil having a pour point below 30 C., preferably below --40 C., having a viscosity of at least 35 est, preferably at least 40 est, at 20 C. It should accordingly have a low content of parafiinic hydrocarbons. The difference between the cloud point and pour point of the mixture should preferably not exceed about 10 degrees of Celcius.

The compressed air tool lubricating oil may contain other additions, such as viscosity index improving agents, extreme pressure agents, inhibitors of different kinds and cloud point and/ or pour point depressants.

The following example is illustrative of a preferred embodiment of the present invention. It should be understood that the example is not intended to limit the invention and that obvious changes may be made by those skilled int he art Without changing the essential character istics and the basic concept of invention.

Example A compressed air tool lubricating oil was made up by mixing together:

Percent by vol.

Spindle oil 50 Di- (Z-ethylhexyl) -sebacate 50 The oil had the following analysis:

Specific gravity at 20 C. 0.904

The lubricating oil has been tested in a compressed air tool under standardized conditions. In this connection, it has been found fully superior to other oils on the market for the same purpose.

The term consisting esentially of as used in the following claims is meant to include compositions containing the named ingredients in the proportions stated and any other ingredients which do not destroy the usefulness of the compositions for the purposes stated in the specifica- .tion.

I claim:

1. A method for the lubrication of compressed air tools, which comprises mixing with the air supplied to the tool a sufiicient quantity of a composition consisting essentially of at least one member selected from the group consisting of diesters of dibasic aliphatic and cycloaliphatic carboxylic acids, containing from 6 to 10 inclusive carbon atoms with monovalent aliphatic alcohols, and a high antifreeze ing quality mineral oil.

2. A method in accordance with claim 1, wherein the diester is 25 to 80 percent, by volume, of the composition utilized.

3. A method in accordance with claim 1 wherein the diester is to percent, by volume, of the composition utilized.

4. A method in accordance with claim 1 wherein the mineral oil is a spindle-type oil having a pour point below -30 C. and a viscosity of at least 35 cst. at 20 C.

5. A method in accordance with claim 1 wherein the diester contains from 5 to 11 inclusive carbon atoms.

6. A method in accordance with claim 5 wherein the diester is di-(2-ethylhexyl)-sebacate.

7. A method in accordance with claim 1 wherein the composition utilized contains a surface active hydrophobing agent.

References Cited by the Examiner UNITED STATES PATENTS 2,222,487 11/ 1940 Oosterhout et a1 252--56 2,718,502 9/1955 Frances et a1. 252--.-49.9 3,053,768 9/ 1962 Cupper 25256 3,130,818 4/1964 Smith et al. 91-46 DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner. 

1. A METHOD FOR THE LUBRICATION OF COMPRESSED AIR TOOLS, WHICH COMPRISES MIXING WITH THE AIR SUPPLIED TO THE TOOL A SUFFICIENT QUANTITY OF A COMPOSITION CONSISTING ESSENTIALLY OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF DIESTERS OF DIBASIC ALIPHATIC AND CYCLOALPHATIC CARBOXYLIC ACID, CONTAINING FROM 6 TO 10 INCLUSIVE CARBON ATOMS WITH MONOVALENT ALIPHATIC ALOCOHOLS, AND A HIGH ANTIFREEZING QUANTITY MINERAL OIL. 